Specifications

1 - 8
1.1.4 Outline design of positioning system
The outline of the positioning system operation and design, using the QD75, is
shown below.
(1) Positioning system using QD75
Positioning module
QD75
Drive unit
Servomotor
Setting
data
PLC
CPU
Forward run
pulse train
Reverse run
pulse train
Deviation
counter
D/A
converter
Speed
command
Servo
amplifier
Interface
M
PG
Feedback pulse
Read, write, etc.
Read, write, etc.
Read, write, etc.
SW D5C-QD75P
Peripheral
devices
interface
Personal computer
Program
Fig. 1.2 Outline of the operation of positioning system using QD75
(a) Positioning operation by the QD75
1) The QD75 output is a pulse train.
The pulse train output by the QD75 is counted by and stored in the
deviation counter in the drive unit.
The D/A converter outputs an analog DC current proportionate to the
count maintained by the deviation counter (called "pulse droop"). The
analog DC current serves as the servomotor speed control signal.
2) The motor rotation is controlled by the speed control signal from the drive
unit.
As the motor rotates, the pulse generator (PG) attached to the motor
generates feedback pulses, the frequency of which is proportionate to the
rotation speed.
The feedback pulses are fed back to the drive unit and decrements the
pulse droop, the pulse count maintained by the deviation counter.
The motor keeps on rotating as the pulse droop is maintained at a certain
level.
3) After the QD75 terminates the output of a pulse train, the motor
decelerates as the pulse droop decreases, and stops when the count
drops to zero.
Thus, the motor rotation speed is proportionate to the command pulse
frequency, while the overall motor rotation angle is proportionate to the
total number of command pulses output by the QD75.
Therefore, when a movement amount per pulse is given, the overall
movement amount can be determined by the number of pulses in the
pulse train.
The pulse frequency, on the other hand, determines the motor rotation
speed (feed speed).